Nonmetallic sheath cable



Api'il 28, 1942. w c, ROBINSON ETAL 2,281,111

NONMETALLIC SHEATH CABLE Filed Sept. 25, 1939 2 Sheets-Sheet 1INVEQITORS Wall/M 6 WW Md WW 7/ 6 704 0 April 28, 1942. w. c. ROBINSONETAL 'NONMETALLIC SHEATH CABLE Filed Sept. 25, 1939 2 Sheets-Sheet 2bmwwp, m wwz. L L L Patented Apr. 28, 1 942 N ONMETALLIC SHEATH CABLEWilliam C. Robinson,

W. E. Moore, tional Electric ration of Delaware Sewlckley, Riverdale, N.12, ossirnors to Na- Products florporatlon, a corpo- Pa., and RalphApplication September 23, 1339, Serial No. 296,236

(Cl. lidilt) 2 Claims.

This invention relates to non-metallic sheath cable of the sort usedalternatively to metallic armored cable in housing electricalconductors.

The invention consists in a. novel organization of wrapping and bindingstructures included in the sheath of the cable, to give improvedcoherence and endurance to the cable.

The structure which has become the generally accepted one for uonmetallic sheath cable is to surround the insulated conductors includedin the cable with o. wrapping of crumpled paper, :iu r h r suitablefibrous material, to ere ty of filler strings of jute or paper y theconductors, to surround this and with a. braided, slop-mend toimpregnate that enposition, it is of advantage that it maybe workedaround obstructions. In such operation, however, the cable isnecessarily subjected to severe kinking, e., flexion about a pluralityof relatively short hon-coincident radii, and to rubbing against sharpor abrasive edges or surfaces.

.It is of importance, therefore, that non-metallic sheath cable have a.sheath so made that it is capable of maintaining its protection of theconductors under such severe conditions without detriment to itsadvantageous quality of flexibility.

We have attained by our invention a sheath structure in. a. non-metallicsheath cable which is very flexible, and. which includes a. fibrouselement so formed and arranged that it is thoroughly saturated with andbonded by a heavy viscous and adhesive flame-retardant saturant. We alsohave succeeded in so organizing the fabric element of the sheath that,under all conditions to which the cable is normally subjected in use, itfirmly supports an outer skin, or capsule, of pitchy flame-retardant andlubricating materials.

In non-metallic sheath cable our invention consists in constructing thesheath of the cable with all a double lever serving or helical wrapping,which replaces the braided, or limit, structure usually included in thesheath of cable of that sort. The two servings, or layers of serving, weapply in opposition to such other so that the outer serving binds theturns of the inner serving against opeui: g relatively to such other,and arrange the outer se. at such single to the longitudinal axis of thecable e whole that it eble to endure severe of th cable without bred!-so, we so the two servings that a Wtively heavy viscous adhesivesuturant is enabled to the outer serving to the o to bee ti". twoservings to such iuuer rving by crossing of on the outer serving isensist tendency for the turns of cg relatively open. This open alsomeasure counteracted by -st the outer serving is of larger size theinner serving and is less the assembly, so it secs modste itself tosevere fiexiou of the cable to an extent adequate to prevent its turnsfrom parting the pitchy outer coating of the sheath which provides a,lubricating and fieme-retardent encapsulation for the cable as a, whole.The several elements going into the sheath of our hon-metallic sheathcable are thus cooperative in protecting each other from injury ordisplacement. I g in the occompenying drawings Fig. l is s schematicview showing in elevation apparatus for applying e double opposedserving in making up the sheath oi the non-metallic sheath cable. Fig.ll: is s. fragmentary elevational view, showing the various cableelements progressively broken sway to expose to view all the saidelements, but omitting any showing of seturent for the structuralelements or of a protective outer coating for the cable; the cable shownin this figure of the drawing being of the oval type, and containing twoconductors. Fig. III is a. cross-sectional View through the innerportion of the cable assembly as organized in the manner illustrated inFig. II, taken in the plane of the section line lH-III of Fig. II. Fig.IV is a fragmentary elevation similar to Fig. II in its showing, but inwhich the cable is illustrated as circular in cross-section and ascontaining three conductors. the inner portion of the cable assemblyshown in Fig. IV, taken in the plane of the section line VV of Fig. IV.Fig. VI is a fragmentary View Fig. V is a cross-sectional view of 2 of acompletely served cable without outer coat ing, and with the outerserving regionally broken away to expose some of the turns of the innerserving. Fig. VII is a fragmentary elevational view of the innerassembly of a cable, showing 5 the preferred form of conductor forinclusion in I our cable, the view showing the conductor elements brokenaway progressively in a manner to sofar as our present invention isconcerned may be braided, knit, or served. Around and between theconductors l and 2 there are windings of crumpled paper and a tubularpaper. dam is wound about both the conductors to form the inner assemblyof the cable. Extending longitudinally cf the conductors withinthe paperdam there are filler and spacer lengths of loosely twisted Jute. Thestructural basis of the cable sheath is formed of two servings 3 and 4.In the drawings the inner serving 8, being designated simply as servingand the outer serving 4,, being designated as "binding? As will be laterexplained, the inner serving may be considered to be a sealing wrap, andthe outer serving may be considered a binder and protector wrap.

' In Figs. IV and V the general organization is similar to that shown inFigs. II and 111, but the cable contains three conductors 5, 8 and 5within the servings 0 and 9. The conductors are braided 40 together asappears in Fig.1V, and the cable as a whole is circular in crosssection.

As appears in both Figs. 11 and IV of the drawings, the inner or sealingwrap of serving is laid to form a lesser angle with the longitudinalaxis of the cable than is the angle formed with the longitudinal axis ofthe cable by the outer binder and protector wrap of. the assembly. Inboth figures of the drawings, the lead of the serving which forms theinner sealing wrap is shown as forming an angle of approximately withthe longitudinal axis of the cable to have a correspondingly great leadwhile the hinder or protector wrap is served at an angle ofapproximately to the longitudinal axis of the conductor to have a lesserlead thereon. It is important in the cable that the serving which formsthe binder wrap be laid to form a greater angle with the longitudinalaxis of the conductor than does the serving which forms the inner,sealing wrap. In view of the great stresses to which the binderandprotector wrap is subjected. it is important that the outer serving belaid to form an angle equal to, or greater than 60 to the longitudinalaxis of-the cable. I

We have discovered that, in addition to advantages derived by diversityin the angular positioning of the two servings, there is substantialadvantage in having diversity in the size of the' strand used in the twoservings and diversity in the compacting of the two servings in theirassembly in the sheath structure. One reason behind this advantage willappear when it is considered that the inner serving acts in the sheathassembly as a sealing wrap, and acts not only as the chief agencymechanically confining the inner assembly of the cable, but also is anelement of primary importance in the cable from the viewpoint offiame-retardance and the viewpoint of general electrical insulation.

In manufacturing the cable, the servings of the sheath are impregnatedwith a relatively heavy, viscous, and adhesive saturant havingflame-retardant qualities. In order that the saturant. may penetrate tothe served sealing wrap, fully and uniformly to impregnate it, it mustpass through the binder and protector wrap lying outwardly of the innersealing wrap. If then the strands of the binder serving be of greatersize than those of the inner wrap, and less compacted in the assembly,even though the turns be firmly in contact with each other, the saturantpenetrates the relatively loose structure of the strands in a volume anddistribution adequate fully and uniformly to impregnate the sealingwrap, so that it forms a uniformly effective electrically insulating andflame-retardant seal about the inner assembly of the cable.

0n the other hand, the binder wrap, lying outwardly of the sealingwrap,- is

itself fully impregnated, and is by the saturant caused to adhere to theinner, sealing wrap of the sheath assembly. Its strands being largerthan those of the sealing wrap, it is the better able mechanically toprotect the sealing wrap and to maintain the integrity of the cablestructure.

Referring to Figs. 11 and IV of the drawings, it is to be understoodthat the strands of the binder wraps 4 and l of the cables therein shownare of greater diameter than the strands 3 and 8 which are served aboutthe inner assembly to form the sealing wraps; and that being applied ineach instance outside the sealing wrap the binder wrap serves toincrease the compacting effect incident to the tension of the sealingwrap as it is served. The material of the strands in both servings ofthe cable sheath is such that they are capable of absorbing thesaturant, being commonly of a twisted fibrous material such as cotton orpaper.

; The saturant may be any one of various compositions commonly sold andused for the purpose of impregnating the fibrous structure of conductorsand cables. Usually it is a composition of asphalt. non-mineral pitch,such as stearin pitch,

and a suitable wax, such as montan wax. Outside the structural assemblyof the sheath there is applied a coating of material, which may begenerally similar to the saturant in its composition but which desirablycontains a higher proportion of pitch.

The general steps of making the cable, chronologically stated, are tomake the inner assembly of the conductor, including jute fillers andpaper wrappers, to apply the opposed serving which forms thesealing wrapand the binder and protector wrap to saturate the served assembly, to

I apply the pltch outer coating, and to apply a finishing coat ofmaterial such as wax. or waxy composition, to give the cable apermanently lubricated surface.

Fig. I of the drawings is generally illustrativev of the manner in whichboth wraps desirably are served. In that schematic view twobobbin-carrying heads II and II are rotatable about the inner cableassembly, designated by reference letter A, as it progresses axiallythrough them. Each of the heads carries a plurality of bobbins, eightbobbins being shown on each head and the bobbins for the two heads Itand II being designated respectively by reference numerals l2 and andprotector I l3. The heads are oppositely rotated to lay the two servingsin opposed helical wrappings one over the other, the head II acting uponthe inner assembly thecable after the head III has applied the innersealing wrap thereto.

In order that both servings be laid in the same progressive operation,to give full coverage in both the sealing wrap and the binder andprotector wrap, accommodation must be made to the different angles atwhich the two servings are laid and the different size of the strandsin. the two servings. The head H is rotated faster than the head ID, inorder that the outer serving which forms the binder and protector wrapmay be laid at a greater angle to the longitudinal axis of the cablethan is the inner serving. Accommodation to this variance may be made bymounting a different number or bobbins on the two bobbin-carrying heads,or ii. the number of bobbins on the two heads be (as shown) equal,accommodation may be made by taking a greater number of ends from eachof the bobbins l2 on head l0 than from the bobbins l3 on head H. Therelationships given below may be taken as illustrative of thosesatisfactorily employed by us in structurally organizing the sheathstructure of several cables. It should be noted that this table givesthe total number of ends of the strands applied by each winding head ineach of its revolutions, and does not divide this total into the numberof bobbins on each:

Angle Size yarn No. of R. P. M. with in strands ends head cable axisDegrees Sealing wrap l0l 48 200 51 llinder wrap 12-2 24 381 68 Sealingwrap l0-l 48 200 51 Binder wrap. 16-2 28 381 68 Sealing wrap... 10-1 4820:) 54 Binder wrap. l22 24 381 70 Sealing wrap, 10*1 48 200 54 llinderwrap l lt-2 28 381 70 In the table -1 means No. 10 yarn. in a singlestrand, and 12-2 means No. 12 yarn in adouble strand. It will be notedthat the double strand of the binder and protector wrap is in eachinstance greater in size than the single strand of the sealing wrap, andthat a lesser number of ends is applied. In both the sealing wrap andthe binder wrap the strand is applied under tension, and tensioningmeans it and iii are indicated for each of the winding heads iii and ii.Both wraps fully and closely cover the structure which they overlie, butthe binder wrap is applied to an underlying structure oi greaterdiameter than that about which the sealing wrap is wound. The strand ofwhich. it is formed is thus unwound more rapidly from the bobbins whichcarry it than is the strand forming the sealing wrap from its bobbins,and there is thus a tendency less severely to compact it as it isserved, Also, the binder and protector wrap, by being served around thesealing wrap, tends to flatten out the sealing wrap, and thereby longitudinally to compact its turns one with the other.

It will be understood that the structural coherence of the sheath in ourcable assembly is greater than that of a cable sheath organized with abraided structure. It is also of importance that the continuity of theinsulation is in our assembly superior to that existing in anon-metallic sheath cable in which the sheath contains a braidedenvelope. This is because a saturant of relatively heavy and viscoussort may effectively penetrate the binder and protector wrap, throughthe relatively uncompacted structure thereof, in such volume anddistribution as fully and smoothly to impregnate the sealing wrap.

In a sheath containing two braided structures there is, on the contrary,a. tendency for the saturant to penetrate at intervals between crossedstrands of the outer braid, unequally to spread in and non-uniformly toimpregnate the inner braid.

It will be noted that the conductors I and 2, shown in Fig. II ofgthedrawings, include braided envelopes, and that this is true also 01' theconductors 5, 6 and I. as shown in Fig. IV of the drawings. On thecontrary the conductor ll, which appears in Fig. VII of the drawings, isa conductor of a structure which is preferred by us, being made inaccordance with the disclosure of our co-pending application Serial No.181,910, filed December 27, 1937, upon which Patent No. 2,222,555,issued November 19, 1940, and our Serial No. 224,522, filed August 12,1938. This conductor i4, shown in Fig. VII, has its core sur-- roundedby a helical serving l5 having its turns locked in position by a binderfilament I6 laid helical ly in opposition to the lay of the serving. Thepurpose of showing conductors of these two diverse sorts is toillustrate that the structure of the cable sheath bears no essentialrelation to the specific form of conductors included in the cable,

ill

and incidentally to illustrate that the conductor of our cc-pendingapplications may suitably be so included.

In Fig. VI of the drawings, the inner and outer servings as designatedrespectively by reference letters B and C, for the reason that the cableas a whole may be either of the form shown in Figs. II and III or theform shown in Figs. IV and V. This figure of the drawings indicates themanner in which the turns of the two servings shift slightly in ilexionof the cable, withoutbecoming Widely separated at any point. Itindicates how this effect occurs by action of the two serving layerssubstantially as a single integrated structure.

We claim as our invention:

1. n non-metallic sheath cable constructed with an inner assemblyconsisting of a plurality of conductors and insulating packing and anexterior non-metallic insulating and protective sheath; a sheathcomposite of an inner sealing wrap or absorbent strands laid in a singlelayer helical serving, and an outer binder and protector wrap ofabsorbent strands greater in size than the strands of the sealing wraplaid as a single layer helical serving with a lesser number of turnsthan the sealing wrap in a helix opposite in sense to that in which theturns of the sealing wrap are laid and with a lesser lead, the saidbinder and protector wrap by its lesser lead forming with thelongitudinal axis of the cable an angle greater than that formedtherewith by the turns or the sealing wrap, the said two wraps beingsaturated and bonded together by a heavy viscous and ad- 4 aaeaui thestrands of the sealing wrap laid as a single layer helical serving witha lesser number of turns than the sealing wrap in a helix opposite insense to that in which the turns of the sealing wrap are laid and withits turns in contact with each other but less severely compactedlongitudinally oi the cable and being physically in condition forfacilitated penetration of saturant throughthe outer wrap ot theassembly to the inner wrap thereof, the binder and protector wrap beinglaid with a lesser lead than the lead of the inner sealing wrap to formrelatively a greater angle with the longitudinal axis of the cable,thetwo said wraps being saturated and bonded together by a heavy viscousand adhesive insulating saturant.

WIILIAM C. ROBINSON. RALPH W. E. MOORE.

